2023 day 09

2023/09/part2/cmd/main.go

@@ -0,0 +1,36 @@
+
+package main
+
+import (
+	"bufio"
+	"os"
+	"fmt"
+	"git.tristans.cloud/tristan/aoc/2023/09/part1"
+	"git.tristans.cloud/tristan/aoc/2023/09/part2/part2"
+)
+
+func main() {
+	reader := bufio.NewReader(os.Stdin);
+	total := 0;
+	for {
+		line, err := reader.ReadString('\n');
+		if (err != nil) {
+			break
+		}
+		values, err := part1.LineConv(line)
+		if err != nil {
+			fmt.Println(err)
+			return
+		}
+		next, err := part2.Next(values, true)
+		if err != nil {
+			fmt.Println(err)
+			return
+		}
+		total += next;
+		fmt.Printf("%v => %v\n", values, next)
+	}
+	println(total)
+	return
+}
+

2023/09/part2/part2/part2.go

@@ -0,0 +1,28 @@
+
+package part2
+
+import (
+	"errors"
+	"git.tristans.cloud/tristan/aoc/2023/09/part1"
+)
+
+func Next(src []int, dir bool) (int, error) {
+	if len(src) < 2 {
+		return 0, errors.New("not enough data!")
+	}
+	if part1.IsZero(src) {
+		return 0, nil
+	}
+	deriv := part1.Deriv(src)
+	nextDelta, err := Next(deriv, dir)
+	if (err != nil) {
+		return 0, err 
+	}
+	if dir {
+		return src[0] - nextDelta, nil
+	} else {
+		return src[len(src)-1] + nextDelta, nil
+	}
+}
+
+

2023/09/part2/part2/part2_test.go

@@ -0,0 +1,19 @@
+
+package part2
+import (
+	"testing"
+	"reflect"
+)
+
+func TestPrev(t *testing.T) {
+	next, err := Next([]int{0,1,2,3}, true)
+	equal(t,err,nil)
+	equal(t,next,-1)
+}
+
+func equal(t *testing.T, actual any, target any) {
+	if !reflect.DeepEqual(actual, target) {
+		t.Errorf("expected %v, got %v", target, actual)
+	}
+}
+